Polymerization of 1,1-disubstituted alkene compounds are typically performed in bulk state, and frequently in situ, such as when monomer is placed between two substrates to be adhered. The resulting polymerization process may be difficult to control resulting in variable performance or mechanical properties. For example, the polymerization process may be characterized by one or more spikes in temperature during the polymerization process, such as by an increase in temperature of about 15° C. or more, about 30° C. or more, or even about 45° C. or more (e.g., during a polymerization reaction). Such an increase in temperature may occur in a short time period (e.g., less than 10 minutes, less than 3 minutes, or even less than 1 minute). Typically, the resulting polymer may be characterized by one or more of the following: a generally high level of branching, a high polydispersity index, a high concentration of non-polymer reaction products, a generally high viscosity, or a generally high molecular weight. For example, when polymerized in bulk, the resulting polymer may have a high viscosity that makes further processing and/or handling difficult.
As used herein, bulk polymerization refers to the polymerization of a polymerizable composition including one or more monomers where the concentration of the one or more monomers is about 80 weight percent or more, preferably about 90 weight percent or more (e.g., about 100 weight percent), based on the total weight of the compounds in the polymerizable composition that are liquid at room temperature.
Polymerization of 1,1-disubstituted alkene compounds using anionic polymerization processes are useful in the bulk polymerization of 1,1-disubstituted alkene compounds and processes which can operate at or near ambient conditions (starting conditions) have been disclosed. Such anionic bulk polymerizations may be initiated using a wide range of initiators, and may even be initiated by contact with certain substrates or by UV light. However, as discussed above, the bulk polymerization may limit the ability to control the structure of the polymer molecules and/or to be able to easily handle the resulting polymer composition or product. These difficulties in bulk polymerization may be particularly pronounced when manufacturing large quantities of polymer, where heat transport issues may occur, especially when there may be shear heat generated by the flow of the high viscosity polymer.
Bulk polymerization of 1,1-disubstituted alkene compounds also present a challenge when attempting to control the structure of the polymer by including one or more comonomers. For example, the high viscosity of the intermediate polymer may present difficulties in preparing a block copolymer (such as by sequential addition of a first monomer system followed by a second monomer system into a reaction vessel). Other problems may arise when attempting to control the structure of a random copolymer, where the reaction rates of the different monomers differ so that the monomers are not uniformly distributed along the length of the polymer molecular. For example, copolymers including one or more 1,1-disubstituted alkene compounds prepared by bulk polymerization are typically expected to have a generally blocky sequence distribution and/or result in polymer molecules having a broad distribution of monomer compositions. As used herein, a copolymer having a generally blocky sequence distribution of monomers may be characterized as having a blockiness index of about 0.7 or less, about 0.6 or less or about 0.5 or less, or about 0.4 or less.
Although emulsion polymerization processes have been employed in free radical polymerization process (see for example, U.S. Pat. No. 7,241,834 B2) to better control the polymer architecture, such processes have not generally been employed in anionic polymerization. In emulsion polymerization systems, the polymerization typically occurs in small micelles that are distributed throughout a carrier liquid (generally water). An emulsifier typically separates the monomer/polymer in the micelles from the carrier liquid. However, in anionic polymerization, many monomers that are capable of polymerization via anionic polymerization are also reactive with water. For example, a Michael addition reaction between 1,1-disubstituted alkene compounds and water is a known reaction which destroys the double bond so that the monomer is no longer polymerizable using anionic polymerization across the double bond. As such, there is a general preference to avoid using water or to diminish the presence of water in the reaction. Similarly, there is a possibility of a Michael addition reaction between the 1,1-disubstituted alkene compound and various surfactants. For these reasons, emulsion polymerization of 1,1-disubstituted alkene compounds has typically been avoided and assumed unsuitable in emulsion polymerization.
When an emulsion polymerization system is employed with free radical polymerization methods, sub-ambient temperatures (e.g., less than 10° C., less than 0° C., or less than −20° C. are typically required to control the reaction. As such, in emulsion polymerization systems it may be necessary to use a carrier liquid that has a low freezing point below −5° C. (such as a mixture of water and a glycol).
Additional difficulties in polymerization of 1,1-disubstituted alkene compounds arise from the possibility of the anionic group of the growing polymer reacting with an acid thereby terminating the reaction. Therefore, one would avoid using an acid in polymerizing 1,1-disubstituted alkene compounds using anionic polymerization.
Prior attempts at anionic polymerization emulsion processes generally have had one or more of the following drawbacks: (1) requirement that the systems have low polymer concentrations (e.g., about 2 weight percent or less, based on the total weight of the emulsion system), (2) have resulted in a prevalence for particle aggregation (even in drop-by-drop methods), (3) have lacked reproducibility for controlling molecular weight distribution, (4) have undesirable reactant by-products, or (5) employ a low reaction temperature.
There is a need for polymerization methods, systems, and resulting polymer compositions or products that allow for improved control of one or more of the following properties of a polymer containing one or more 1,1-disubstituted alkene compounds: the weight average molecular weight, the number average molecular weight, the polydispersity index, the zero-shear viscosity of the polymer (e.g., at one or more temperatures of at least about 20° C. above the melting temperature of the polymer), the viscosity of the polymer system (e.g., the bulk polymer or the polymer emulsion) at room temperature, the sequence distribution of monomers in a random copolymer, or having at least two different polymer blocks covalently bonded (e.g., each containing one or more 1,1-disubstituted alkene compounds). There is also a need for polymerization process which can be scaled-up (e.g., to a reactor of about 20 liters or more, or having a throughput of about 10 kg of polymer per hour or more. There is also a need for processes that result in an emulsion. Such emulsion may be useful for applications such as paints, coatings, finishes, polishes, and adhesives. For example, there may be a need for process and polymer systems that result in an emulsion having a controlled size of emulsion particles.